Detergents are necessary components of engine oils for both gasoline and diesel engines. Incomplete combustion of the fuel produces soot that can lead to sludge deposits, as well as carbon and varnish deposits. In the case of diesel fuel, residual sulfur in the fuel burns in the combustion chamber to produce sulfur derived acids. These acids produce corrosion and wear in the engine, and accelerate the degradation of the oil. Neutral and overbased detergents are added to engine oils to neutralize these acidic compounds, thereby preventing the formation of harmful engine deposits and dramatically increasing engine life.
Metal detergents represent a major source of ash in formulated engine oils. Alkaline earth sulfonates, phenates and salicylates are typically used in modern engine oils to provide detergency and alkaline reserve. Low metal detergents are desirable for reducing ash and reducing sulfur is desirable for environmental reasons among others. Phenates often used in lubricating oil typically contain sulfur and reducing or eliminating their use is also desirable.
U.S. Pat. No. 5,330,666 discloses a lubricant oil composition useful for reducing friction in an internal combustion engine which comprises a lubricating oil basestock and an alkoxylated amine salt of a hydrocarbylsalicylic acid.
U.S. Pat. No. 5,688,751 discloses that two-stroke cycle engines can be effectively lubricated by supplying to the engine a mixture of an oil of lubricating viscosity and a hydrocarbyl-substituted hydroxyaromatic carboxylic acid or an ester, unsubstituted amide, hydrocarbyl-substituted amide, ammonium salt, hydrocarbylamine salt, or monovalent metal salt thereof in an amount suitable to reduce piston deposits in said engine. The mixture supplied to the engine contains less than 0.06 percent by weight of divalent metals.
U.S. Pat. No. 5,854,182 discloses dispersible magnesium borate overbased metallic detergent with an extremely fine particle prepared by reacting a neutral sulphonate of an alkaline earth metal with magnesium alkoxide and boric acid under anhydrous conditions in the presence of a dilution solvent followed by distillation to remove alcohol and part of dilution solvent, cooling the reaction mixture and filtering.
U.S. Pat. No. 6,174,842 discloses a lubricating oil composition that contains from about 50 to 1000 parts per million of molybdenum from an oil-soluble molybdenum compound that is substantially free of reactive sulfur, about 1,000 to 20,000 parts per million of a diarylamine, and about 2,000 to 40,000 parts per million of a phenate to reduce oxidation and improve deposit control.
U.S. Pat. No. 6,339,052 discloses a lubricating oil composition for gasoline and diesel internal combustion engines comprising an oil of lubricating viscosity; from 0.1 to 20.0% w/w of a sulfurized, overbased calcium phenate detergent derived from distilled, hydrogenated cashew nut shell liquid; and from 0.1 to 10.0% w/w of an amine salt of phosphorodithioic acid derived from cashew nut shell liquid.
U.S. Pat. Nos. 2,497,521 and 2,568,472 disclose oil compositions comprising an amine salt of a compound formed from boric acid and a certain hydroxy carboxylic acid. U.S. Pat. No. 3,239,463 discloses a tertiary alkyl primary amine salt of a tetra-covalent boron acid as an additive for lubricating oil. The tetra-covalent boron acid is prepared by reacting boric acid with a polyhydroxy compound or hydroxycarboxylic acid, e.g., salicylic acid which is then stabilized by formation of the amine salt.
U.S. Pat. No. 7,691,794, incorporated herein by reference, discloses the reaction products of an acidic organic compound, a boron compound and an alkoxylated amine and/or an alkoxylated amide, and fuel and lubricant compositions comprising these reaction products.
There is still a need to lower the amounts of sulfur, phosphorus and ash in lubricant formulations. It has been found that the combination of certain low ash detergents with commercially available overbased calcium sulfonates provides excellent lubricant detergency while eliminating the need for phenates and reducing the levels of ash, phosphorus and sulfur.